1. Field of the Invention
This invention relates in general to electrical melting furnaces and in particular to a new and useful contact electrode assembly and to a method of exchanging it for an electrical melting furnace.
The invention relates particularly to a direct current arc or resistance melting furnace, in particular an exchangeable contact electrode arrangement, the contact electrode comprising a metal support plate, a metal base plate spaced from and connected with the support plate by bolts, one or more metal contact rods having neck portions fastened to the base plate, a refractory tamping between upper contact rods mounted over the base plate and arc support plate, and current and coolant lines arranged below the base plate on the exchangeable electrode arrangement.
During operation of an alternating current arc furnace, reactions to the current supply network occur in the form of asymmetries and flicker. Various possibilities for damping these phenomena are known, inter alia the operation of the arc furnace as a direct current furnace. Through the progress made in the development of semi-conductor components the prerequisites have been created in recent years for the construction of appropriate rectifiers.
The operation of an arc furnace as a d-c furnace with a cathode-poled graphite electrode and an anode-poled contact electrode in the furnace bottom further offers the advantage of considerably reduced graphite electrode consumption. An additional advantage is the clearly lower noise level.
The design and operation of d-c furnaces are known from many publications. The structural part essential to the practical operation of the furnace is the contact electrode in the furnace tank, which must ensure both good electrical contact with the charged scrap or, in the subsequent melting process, with the liquid metal, and must also withstand high thermal load.
A similar contact electrode is known from DE-PS 31 06 741.
The contact electrodes in the d-c arc furnace are subject to wear earlier than the furnace hearth lining. Since the changing of individual contact rods requires substantial labor, the method has been adopted of exchanging all contact rods jointly at appropriate intervals of time.
In the procedure followed until now, a suitable pulling lug was placed in the small amount of residual melt remaining in the furnace, after the last melt. After its cooling and solidification, the residual melt, contact rods and lining can then be pulled by means of a suitable device. Thereafter new contact rods are inserted and the center of the furnace bottom is tamped anew.
This procedure has the drawback that insertion of the contact rods, tamping of the center of the furnace bottom, and the following drying of the taping composition, delay the restarting of the furnace. Also tamping of the center of the furnace bottom inside the hot furnace is difficult for the personnel.